Find an equation of a parabola that has curvature 8 at the origin.

Since we know its a parabola and lets just assume it opens upwards and has origin (0,0) then the equation has to be f(x)=a(x^2). Too find value a, we have to use equation 11 in the textbook. 
k(x)= | f''(x) |/ [1+(f'(x))^2]^(3/2) 
where | f''(x) | = 2a and f'(x) = 2ax 
U then simplify equation and use k(0) to get the 
k(0) = 2a, but in the question k(0) = 8, so 8=2a, and a is equal to 4, so equation is 4x^2